Various freeze processes have been developed to produce potable water from seawater or brackish water, to concentrate fruit juices such as orange juice and grape juice, vegetable juices such as tomato juice, coffee, and to separate dissolved or suspended salts from the liquid carrier. See, for example the United States patents of Ashley et al U.S. Pat. No. 3,070,969; Ashley U.S. Pat. No. 3,477,241; Ashley U.S. Pat. No. 3,501,924, Ganiaris U.S. Pat. No. 3,620,034, Johnson U.S. Pat. No. 3,664,145 and Ogman U.S. Pat. No. 4,091,635.
One of the major problems in freeze concentrating a liquid mixture has been the deposition of frozen solvent, usually ice, on the freeze exchanger surfaces. Build-up of ice lowers heat transfer and reduces the efficiency of the apparatus. In addition, if build-up of ice or some other frozen solvent continues it can plug up the apparatus completely making it necessary to shut it down to thaw out the frozen material.
One type of freeze exchanger recently developed employs a tube and shell arrangement. Cooling fluid flows around the tube while a film of liquid to be concentrated flows downwardly along the inside surface of the tube. By indirect heat exchange the liquid feed is cooled and crystals of the solvent or liquid carrier, often water, are formed. To prevent build-up of ice, the metal tube inside surface is highly polished by a electro-polishing or chemical polishing procedure. The protracted use of such equipment in concentrating liquid mixtures can be expected to result in degradation of the polished surface to such an extent that the tube needs replacement. This is a costly operation and involves considerable down-time for the freeze exchanger. A need accordingly exists for a freeze exchanger which can avoid such a problem by permitting ready replacement of the freeze exchanger liquid mixture contacting surface.